Product accumulation systems are routinely used in conjunction with conveyors for the storage and accumulation of products which are fed from an upstream source onto conveyors. In the normal operation of this type system, products are placed on a conveyor at the upstream location, for instance at one operational station, and then transported to a downstream location by conveyor where the next step in the manufacture or distribution of the products is to be accomplished.
It is not uncommon that, during this process, there may be a disruption at a downstream location caused by a malfunction of machinery, some constraining problem, or other circumstance which prevents downstream machine from accepting products. Continued operation of production upstream may result in the build-up of line back pressure which could cause a further problem in permitting the unrestricted movement of products. However, if such a disruption is one which can be addressed relatively quickly, upstream products which normally would be transported to the malfunctioning location, can be received and temporarily stored by an accumulator which is integral to the system.
By employing such an accumulator, the upstream machinery can continue to operate by moving products to the accumulator. Since product movement can continue, there is no build-up of line pressure. Such a system also saves the substantial time and expense which would result in having to shutdown and then restart the entire system, if no accumulator was otherwise available.
As products are being received and retained by the accumulator, the downstream problem can be addressed. When that part of the system resumes full operation, the products stored in the accumulator are released to the downstream destination, with little downtime to the system. Products can also be received and stored at the accumulator in case there is an upstream disruption. In this case, accumulated products could be retained and sent downstream in order to keep the system operational while the upstream problem is being remedied.
There are several types of commonly used accumulator systems which perform the above described functions. However, these systems have significant disadvantages. One such system is an inline conveyor which allows products to build up either in single file or en masse in front of the constraining operation. If the products are stored in single file, the amount of storage is minimal and the build-up of line pressure can be problematic for the downstream machinery, as well as the products, due to damage. If products are stored inline and en masse, the amount of storage is increased, however, the line pressure increases as well and the added requirement of putting the products back into single file is required. This creates the possibility of lost production due to jamming in the single filer.
A second type is offline storage. These devices store excess products at right angles to the line in mass. As products back up on the production line, the storage device will allow product flow out onto the planar surface, which is powered away from the line during the period of accumulation. When the stored products are called for, the planar surface reverses direction and the stored products are loaded back onto the production line. This is almost always done en mass and therefore has the same inherent problems with line pressure and single filing requirements as inline storage devices.
A third type uses re-circulating storage. This type of storage device allows products to travel directly from the entry point to the exit point without interrupting the flow, until a need to store products occurs. When it does, products are re-circulated by means of two planar surfaces moving in opposite directions. Products that cannot exit the storage device are allowed to re-circulate onto the planar surface, moving in the direction which is opposite to the direction of discharge. This technique has been very effective in minimizing the amount of line pressure that can build up, as well as incorporating within the device the inherent ability to single file without a separate device to perform this function. However, due to the planar surfaces being adjacent to each other and the requirement that the products reverse direction at either end of the storage device, there are limitations to the size shape and speed of the products which can be stored on such a device. Product instability limits the application of these devices. Another factor, which limits the use of these devices is the noise and label damage generated by product-to-product contact during the re-circulating process. Products such as larger glass containers and the like create noise levels which are not acceptable in normal production environments.
The limitations and disadvantages of prior accumulator systems have been substantially overcome by the systems described in U.S. Pat. Nos. 6,575,287 and 6,612,425. These systems disclose continuous single path conveyors, uniquely configured to transport products and comprising accumulator sections to accommodate and handle excessive product loads. However, while these single product accumulator conveyors have distinct advantages, there are occasions when dual conveyors are more appropriately used, e.g. for added flexibility in system configuration and to adapt the systems for the movement of different products and product containers.